This application claims priority under 35 U.S.C. xc2xa7xc2xa7 119 and/or 365 to Application No 2002-9767 filed in Korea on Feb. 23, 2002; the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a dielectric device having a multi-layer oxide artificial lattice and a method for fabricating the same, and more particularly to a dielectric device having a multi-layer oxide artificial lattice formed by depositing atomic unit layers or unit lattice layers having a specific alignment so as to improve tunability of a microwave voltage tunable device and dielectric constant of a capacitor for memory and a gate oxide for MOS devices, and a method for fabricating the same.
2. Description of the Related Art
Recently, semiconductor technologies, which are representative technology of late twenty century, make great stride so that the semiconductor technologies become a symbolic meaning of a development of scientific technique. The high speed and large capacitance of semiconductor devices with regard to a CPU and a memory thereof are rapidly achieved. The semiconductor memory is highly integrated above 1 Giga byte (GB) and a high-speed DRAM capable of inputting/outputting data at a high speed of few nano seconds is suggested (Hitachi, Ltd., (TSE:6501) and Elpida Memory, Inc., Japan, Sep., 26, 2001/Kang, tae won, physics and high technology 9 (7/8), 33 (2000)). In order to achieve the high speed and large capacitance of the semiconductor device required for recent information telecommunication society in which large amount of information is communicated, studies regarding to new semiconductor processes and material have been carried out. The studying object is metal oxide. Metal oxide has various crystal structures, so it has various physical features. Accordingly, metal oxide can provide various functions, which cannot be achieved from conventional semiconductor materials and insulation materials. That is, due to its high dielectric constant, metal oxide is widely utilized in a large scaled integration memory, a non-volatile memory, a microwave dielectric for mobile telecommunication part, a high-temperature superconductor, a sensor using a magnetoresistance effect, and an electrode of semiconductor/electronic devices using the conductivity, so it is recently called as xe2x80x9coxide electronic engineeringxe2x80x9d (P. A. Cox, Transition Metal Oxide (Clarendon, Oxford, 1992)).
The development of oxide materials having the high dielectric constant is a main point for the large scaled integration, so the study thereof has been actively carried out. In the future capacitor industry, the next-generation materials having an effective equivalent thickness below 1 nm is required, and a gate insulation film of CMOS (gate size 70 nm grade) also requires the effective equivalent thickness below 1 nm. Among oxide dielectrics, ferroelectric oxide has relatively high dielectric constant, so it is spotlighted and studied in the world as materials for achieving the large scaled integration above Giga grade in DRAM (R. A. Mckee et al., Phys. Rev. Lett. 81, 3014 (1998)/D. E. Kotech, Integr. Ferroelectrics, 16, 1 (1997)). In addition, in order to achieve the large scaled integration and high-speed of CMOS, which is a base structure of a semiconductor, the thickness of a gate insulation film is required to be set below 2 nm. However, as the thickness of the insulation film becomes thin, the quantum effect, such as tunneling effect of electrons, occurs. In order to solve the above problem, ferroelectric materials having the high dielectric constant was recently used as the gate insulation film. Among oxides having the high dielectric constant, oxide having peroveskite structure has been spotlighted. Peroveskite oxide has various physical properties, such as the high dielectric constant, ferroelectric, piezoelectric, and electro-optical properties, so it is widely utilized in non-volatile semiconductor memories, piezoelectric devices, optical telecommunication devices, and superconductive devices, and studies utilizing the peroveskite oxide in the devices has been widely carried out (M. Hong et al., Science, 1897 (1999)). The peroveskite oxide has a simple structure of ABO3 and mainly forms a cubic structure, so the physical properties thereof are easily understood so that it is utilized in various applications. For example, BaTiO3, SrTiO3, (Ba, Sr)TiO3, and (Pb, Zr)TiO3 are used as the peroveskite oxide. However, various electronic and optical devices using the ferroelectrics adopt the above materials existing in nature. Accordingly, the critical phenomenon, which is a basic limit of the ferroelectrics, cannot be overcome. That is, the high-integration and large scaled integration of devices and the nano-scale of materials are limited so that a highly-functional nano device cannot be obtained. To achieve the nano device, besides a conventional material to be used, a dielectric artificial material is required (K. Ueda, H. Tabata and T. Kawai, Science 280, 1064 (1998)). The manufacturing of an oxide artificial lattice is recently studied for obtaining a new superconductive material or a ferromagnetic spin alignment, which cannot be obtained from nature. Accordingly, the oxide artificial lattice becomes a new advanced material allowing the nano-scaled thin film growing technology and materials design (H. Tabata, Tanaka and T. Kawai, Appl. Phys. Lett. 65, 1970 (1994)/E. D. Specht et al., Phys. Rev. Lett. 80, 4317 (1998)).
On the other hand, the recently used telecommunication device, that is a microwave voltage tunable device such as a phase shifter, a tunable filter, and a steerable antenna, requires a high tunability. In case of a conventional microwave voltage tunable device, (Ba, Sr)TiO3 is used as an insulation film formed between metal electrodes, so that a metal-insulator-metal structure is achieved. Then, an electric field of 1 MV/cm is applied to the metal electrodes, and about 74% of the tunability is obtained therefrom (xe2x80x9cComposition-control of magnetron-sputter-deposited (BaxSr1-x)Ti1+yO3+Z thin films for voltage tunable devicexe2x80x9d, J. Im et al. Appl. Phys. Lett. 76. 625). In addition, when a meta-insulator-metal structure is formed by using SrTiO3 thin films, which is an insulation film formed between metal electrodes, about 55% of the tunability is obtained from the electric filed of 1 MV/cm applied to the metal electrodes (xe2x80x9cEffects of strain on the dielectric properties of tunable dielectric. SrTiO3 thin filmsxe2x80x9d, S. Hyun and K. Char, Appl. Phys. Lett. 79, 254).
It is an object of the present invention to manufacture a nano-scaled dielectric (may be semi-stable phase), which does not exist in nature, by forming a dielectric in nano-scale through performing deposition process of an oxide artificial lattice consisting of various atomic stacking sequence with layer-by-layer growth process to overcome the limit of materials existing in nature by growing the artificial material, thereby providing high dielectric constant to a capacitor of tera-level semiconductor memory and a gate oxide of MOS based devices, and also providing high voltage tunability to microwave tunable (or frequency agile) devices.
To achieve the above object, the present invention provides dielectric devices including a multi-layer oxide artificial lattice having a high tunability and dielectric constant and a method for manufacturing the same, wherein an oxide thin film used ma microwave voltage tunable device, dynamic random-access memory (DRAM) OR metal-oxide-semiconductor (MOS) based devices is replaced with the artificial lattice, in which dielectric materials such as BaTiO3 (abbreviated herein as BTO) or SrTiO3 (abbreviated herein as STO) are periodically deposited and grown, thereby compacting the size of the microwave voltage tunable device or memory, and matching with the high speed and high-frequency requirements. When the artificial lattice is formed by forcibly growing the BTO or SSTO atomic layer with layer-by-layer growth, the high voltage tunability (=(Cmaxxe2x88x92Cmin/Cmin)) and high dielectric constant are represented due to the stress applied to an interfacial surface between BTO and STO. Even when the thickness of the thin film is reduced, the property of the oxide artificial lattice can be utilized as a capacitor of the microwave voltage tunable device and a capacitor of memory devices and gate oxide in MOS based devices.
To achieve this and other objects, the present invention provides a method adapted for a dielectric device having a substrate, a dielectric film coated on the substrate so as to be selectively patterned thereon, and an upper electrode deposited and patterned on the dielectric film, or a dielectric device having a substrate, a lower electrode deposited on the substrate so as to be patterned thereon, a dielectric film coated on an upper portion of the lower electrode so as to be selectively patterned thereon, and an upper electrode deposited and patterned on the dielectric film. The dielectric films are constructed by depositing sequentially each consisting layers with one unit lattice thickness (xcx9c0.4 nm) (so called layer-by-layer growth process). The dielectric film is formed by repeatedly depositing at least two dielectric materials having dielectric constant different from each other at least one time in a range of the unit lattice thickness (xcx9c0.4 nm) to 20 nm or by depositing at least two dielectric materials in a predetermined alignment adapted for a functional device, thereby forming one artificial lattice having an identical directional feature.
At this time, the dielectric material to be used is capable of periodically depositing the atomic unit layers including perovskite, tungsten bronze, and pyro-clore structures. Preferably, the dielectric material is any one selected from the group consisting of BaTiO3, SrTiO3, KNbO3, KTaO3, PbTiO3, PbZrO3, and CaTiO3 having a peroveskite structure. More preferably the dielectric material is one of BaTiO3 and SrTiO3 having a peroveskite structure. At this time, a lattice of BaTiO3 is preferably transformed in a c-axis direction within a range of 1.01xe2x89xa6c/axe2x89xa61.05, and a lattice of SrTiO3 is preferably transformed in an a-axis direction within a range of 0.08xe2x89xa6c/axe2x89xa61.0.
In addition, the substrate and the dielectric film have crystal structures having directional features identical to each other. The dielectric film can be utilized as a capacitor of memory devices, a gate oxide of MOS based devices, and a capacitor of the microwave voltage tunable device of which the dielectric constant is varied according to the voltage applied thereto.
On the other hand, according to a method for manufacturing the dielectric device having a multi-layer oxide artificial lattice, the dielectric film is constructed by depositing sequentially each consisting layers with one unit lattice thickness (xcx9c0.4 nm) and is formed by repeatedly depositing at least two dielectric materials having dielectric constant different from each other at least one time within a critical thickness in the repeating period range, capable of maintaining a lattice coherence or a partial coherence, or depositing at least two dielectric materials in a predetermined alignment adapted for a functional device, thereby forming one artificial lattice having an identical directional feature.
At this time, the repeating period of the dielectric material is preferably determined within a range of 0.8 to 20 nm. In addition, the manufacturing process of the dielectric film is any one selected from the group consisting of a pulsed laser deposition process, a molecule beam epitaxial process, a chemical vapor deposition process, a physical vapor deposition process, an atomic layer deposition process and a sputtering process. In detail, the pulsed laser deposition process comprises the steps of setting a deposition temperature in a range of 600 to 700xc2x0 C. while raising the deposition temperature by 10xc2x0 C. per minute and maintaining a partial pressure of oxygen in a predetermined range of 1 mTorr to 300 mTorr, thereby forming a process atmosphere; rotating the substrate at a predetermined speed within a range of 8 to 12 rpm; focusing a laser having 248 nm of wavelength and 30 ns of pulse in a size of 8xc3x972 mm with using KrF gas as a laser source, and inputting targets of BaTiO3 and SrTiO3 having 99.9% purity into the substrate with setting a power intensity of the laser in a range of 1 to 3 J/cm2; performing the deposition process by radiating the laser to the targets at a rate of 1 pulse/sec with setting a deposition speed of the BaTiO3 and SrTiO3 layers in a range of 9 to 13 pulse/1 unit lattice and 11 to 15 pulse/1 unit lattice, respectively; and lowering the temperature of a chamber by 8 to 12xc2x0 C. per a minute while maintaining the partial pressure of oxygen in the chamber at 300 to 500 Torr, after forming the artificial lattice by using BaTiO3 and SrTiO3.